Addendum: and keep in mind that the DR / SNR numbers are calculated based on optimum exposure (to the right), and not based on exposing to the camera's meter. If you expose to the camera's meter with the E-M5, you'll underexpose by about a stop, and the resulting DR will be lower than the maximum possible DR had you exposed optimally to the right.

Ok,

please disregard the "unfair" statement. My only agenda is to try to understand how to interpret this. I want to iterate on your last point: "If you expose to the camera's meter with the E-M5, you'll underexpose by about a stop, and the resulting DR will be lower than the maximum possible DR had you exposed optimally to the right." Now we are getting somewhere. Can you tell me how to calculate how much less the DR would be? Take this point for example:

Measured ISO: 5953

Manufacturer ISO: 12800

Dynamic Range: 7.5Ev

If you expose so as to leave one EV worth of unused headroom above the brightest highlights, the DR of the image would be one EV less (6.5 instead of 7.5 EV).